This application claims priority under 35 USC 119 of Japanese Patent Application No. 2000-83273 filed on Mar. 21, 2000, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a control device for a selective clutch which is applied in a large vehicle, in particular a tractor or the like.
2. Description of the Related Art
Recently, the use of automatic gear changing devices has become widespread in large vehicles such as tractors and trucks in order to reduce the stress on drivers. The most suitable gear speed for the velocity of the vehicle is determined according to a map and a shift up or a shift down is performed automatically as a function of the acceleration or deceleration of the vehicle.
Such automatic gear changing devices are also typically equipped with an autoclutch which engages and disengages a friction clutch using an actuator. In this way, during a gear changing operation, the clutch is automatically disengaged before the gear is disengaged and the clutch is automatically engaged after the gear has been engaged. There is also so-called moving-off control in which the clutch is kept disengaged when the vehicle is in the stationary state, the gear box (transmission) is put into a moving-off gear (gear position suitable for starting of the vehicle) and then the system goes into an acceleration waiting state. After this, when the driver depresses the accelerator pedal, the clutch is gradually automatically engaged.
Some autoclutch devices can perform manual engagement and disengagement using the clutch pedal. In other words, such device is a selective clutch comprising an autoclutch and a manual clutch. The reason for this is to ensure that the clutch can be engaged and disengaged when there is a failure in a solenoid valve of the clutch automatic control or the like or to permit sensitive clutch work at very low travel speeds and the like.
However, if there is interference with the automatic engagement and disengagement operations when the driver selects manual engagement and disengagement of his own accord, there is a risk not only that the vehicle will fail to comply with the driver""s wishes but also that it will sudden starting or the like especially when the vehicle is moving off.
An object of the present invention is to prevent interference with the automatic engagement and disengagement of the clutch when making manual engagement and disengagement selections.
According to one aspect of the present invention, there is provided a control device for a selective clutch that can attain the above object. The selective clutch includes an autoclutch device having a friction clutch, a clutch actuator that disengages and engages the clutch, and a controller that controls disengagement and engagement operations of the clutch by issuing commands to the clutch actuator. The selective clutch further includes a manual clutch device that disengages and engages the clutch in response to depressing and releasing of a clutch pedal. The control device for such selective clutch includes a vehicle velocity detector, a gear speed detector for detecting a gear speed of a gear box, a clutch pedal depression detector, and a second controller for prohibiting clutch disengagement and engagement by means of the autoclutch device or canceling the prohibition on the basis of detection results of said vehicle velocity detector, said gear speed detector and said clutch pedal depression detector. The autoclutch is prevented from automatically disengaging and engaging the clutch under certain circumstances such that the manual clutch disengagement and engagement is given priority over the automatic disengagement and engagement at the time of moving off the vehicle. After the vehicle enters a stable running condition, the prohibition on the automatic disengagement and engagement of the clutch is cancelled.
The second controller may prohibit the clutch disengagement and engagement by the autoclutch device when all the following conditions are fulfilled: the vehicle velocity is zero, a current gear speed or a target gear speed is other than neutral, and a gear speed prior to the current gear speed or the target gear speed is the neutral.
The second controller may cancel the prohibition on the clutch disengagement and engagement by the autoclutch device if a gear changing state is detected, or if the clutch pedal is released and a rotational speed of the friction clutch exceeds a prescribed value suitable for disengaging of the friction clutch. The prescribed value is about 900 rpm.
The second controller may not cancel the prohibition unless the friction clutch rotational speed continuously exceeds the prescribed value for a predetermined period.